Biopolymers: Guide to a Band 6 Answer

These questions are often a source of trouble for HSC Chemistry students. Every student should have a biopolymer which they can name and describe briefly, but often they don’t have enough information for a 5 or 6 mark question. This guide will make sure you are confident to answer any possible question on biopolymers.

Let’s start by looking at the syllabus dot point about biopolymers:

“Use available evidence to gather and present data from secondary sources and analyse progress in the recent development and use of a named biopolymer. This analysis should name the specific enzyme(s) used or organism used to synthesise the material and an evaluation of the use or potential use of the polymer produced related to its properties.”

Let’s start with the simple: you need to be able to name a polymer and the enzyme or organism used to make it, then discuss its properties and uses. The challenging part, however, is hidden in that first sentence: you need to analyse progress in the recent development of the biopolymer. In my experience, this is a significant stumbling block. I hope that after reading this it will become completely straight-forward.

Name of biopolymer

The biopolymer I suggest to use is Polyhydroxybutanoate-co-3-hydroxyvalerate (PHBV). I know it’s a long name, but it is worth remembering!

Method of production

Polyhydroxybutanoate (PHB) is generated by growing the bacteria Alcaligenes eutrophus in a nutrient rich medium and then starving them of nitrogen. The polymer generated is strong but brittle; in order to reduce this, a copolymer with polyvalerate can be produced by growing the bacteria on a medium containing valeric acid. This copolymer is called PHBV.


PHBV is typically strong and only slightly flexible. The ratios of the two monomers can be altered to produce a range of properties from brittle to flexible, allowing it to be similar in properties to polypropylene or high density polyethylene (HDPE). Its structure also makes it biodegradable by bacteria and also in the human body. It is also biocompatible inside the human body and does not activate an immune response.


These properties lead to uses in biodegradable razor handles and bottle-caps. Further, it is ideal for medical sutures (stitches) and other devices, particularly those which are inside the body and will not be removed/retrieved. The material is not rejected by the body and slowly degrades to safe products.

Evaluating its potential

These evaluations always involve splitting the question into chemical potential (can the material technically be used for this purpose) and economic potential (is it cost effective to use for this purpose).

In terms of chemical potential, the answer is quite simple: it is a strong polymer, so is useful in situations requiring durability and low flexibility. Further, the fact that it is biodegradable makes it environmentally superior to the plastics currently used for these purposes.

However, the economic potential is limited. PHBV is significantly more expensive to produce than petrochemical alternatives. Indeed, this is the reason it has failed to become a marketable product. In the current economic climate, lower cost will trump a ‘green’ product almost every time.

As a result, I would evaluate the potential of the polymer as low given its current cost of production and the high availability of cheap alternatives. As oil reserves dwindle or if more effective production methods become available, there is a possibility that PHBV will become a viable option, but under current conditions, it is not.

Progress in recent developments

As I explained earlier, the most overlooked part of this dot point is the progress and development of the biopolymer. However, you do only need 2-3 marks worth of information here. The first point which can be made in the development of PHBV is the addition of valeric acid to improve its properties.

The second key step in the development of PHBV is the insertion of the gene used by A. eutrophus into plants such as maize. This successfully allowed the production of the polymer by plants, improving yield and reducing cost.

While several companies have attempted to produce PHBV on an industrial scale, none have been commercially successful in doing so. However, new research includes investigating the production of PHBV by bacteria in wastewater, both cleaning the water and producing a useful product.


The information above should be sufficient to achieve a band 6 answer to any question on biopolymers. Many students will not be able to answer with this level of detail, allowing you to differentiate yourself.

If you found this helpful, let me know with a comment here or on facebook and share it with your friends who do Chemistry. As always, if there’s another topic you want to see an article or a video (for our upcoming Top Marks QA series) on, let me know!

Tim Mason
General Manager